Emissions code
P0151: Upstream oxygen sensor voltage too low (bank 2)
How this range is built
| Part of the job | Low | High |
|---|---|---|
| Parts | $40 | $180 |
| Labor: 0.6 to 1 hours × $125 to $175 an hour | $75 | $175 |
| Fees: shop supplies, disposal, diagnostics | $0 | $15 |
| Total, rounded | $110 | $370 |
The hourly rate is the BLS Occupational Employment and Wage Statistics, May 2025 average pay for this trade in Boston, $31.54 an hour, times 4 to 5.5 to cover what a shop bills (overhead, tools, insurance, profit). Parts are a band from budget aftermarket to the manufacturer part. Full method.
Not a repair shop, estimates only. Typical range, estimate. Not a quote. Your car, parts and shop change the number.
This is the range for the most common fix, oxygen sensor replacement (one sensor). Which repair your car needs depends on a proper diagnosis.
The oxygen sensor in front of the catalytic converter on the side without cylinder 1 is reporting a voltage so low that it looks like a very lean exhaust. Either the sensor is stuck and not telling the truth, or the engine on that side really is lean from an air leak or low fuel.
- Safe to drive?
- Short trips only
- Most common cause
- Failed upstream O2 sensor
Drive gently. A lean engine can misfire and run hot.
What you may notice
- Rough idle
- Hesitation
- Check-engine light
Common causes, most likely first
- Failed upstream O2 sensor
- Vacuum leak on bank 2
- Exhaust leak near sensor
- Wiring fault
Check this first
With the engine idling, listen for hissing near the intake on the bank 2 side and look for puffs of soot at the exhaust joints. Leaks of either kind are cheaper to repair than a sensor and can cause this code.
Other repairs that sometimes fix P0151
| Repair | Typical range, Boston |
|---|---|
| Vacuum leak repair | $100 to $530 |
| Diagnostic scan (check engine light) | $60 to $290 |
Before you pay
- Ask the shop what test showed this part is the cause, not just that the code appeared.
- Ask for parts and labor listed separately, and for the hours.
- Ask for a written OK before any extra work. Massachusetts rules require written authorization before repairs.
Got a quote already? Check it against the range. Want to see if your car has a recall tied to this problem? Check recalls by VIN.
Need to read a code yourself? OBD-II scanners on eBay (affiliate link, disclosure).
P0151 questions
Is it the sensor or the engine?
Fuel trim readings help decide. If the computer is adding a lot of fuel on that bank, the engine is truly lean. If trims are normal and the sensor still reads low, then the sensor is the problem.
Bank 2?
Bank 2 is the side of the engine that does not hold cylinder 1. On many V6 and V8 engines it is the opposite side from the one with the first cylinder, which the shop can point out.
Will it clear?
Not unless the cause is fixed. Clearing the code only erases the memory. If an air leak or a weak sensor is still there, the light returns after a few drive cycles.
How much does it cost to fix P0151?
The most common fix, oxygen sensor replacement (one sensor), has a typical range of $110 to $370 in Boston. It is an estimate built from parts prices and local labor wages, not a quote. Your car and shop change it.
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Code meaning written in our own words. Some codes mean different things on different makes, so check your scan tool or manual. Not a repair shop, estimates only.